A loading dock for a vehicle such as a trailer truck or box truck commonly includes an overhead door of a width and height sufficient to accommodate the interior region of the trailer cargo area. When the overhead door is open, the truck backs towards the loading dock until the rear of the cargo compartment engages the dock. The cargo compartment of the truck is thus roughly aligned with the opening of the loading dock. The truck may have an overhead door or, more commonly, hinged panel doors that swing open and are stowed against the side of the trailer.
In some loading dock operations, there is a large difference in temperature between the inside of the truck cargo area and the outside environment, or between the interior of the loading bay and the outside environment, or both. For example, a refrigerated trailer may dock to a refrigerated loading bay, and there may be a large temperature difference between the vehicle cargo area/loading bay and the outside environment. The cargo may include perishable items or items required to be kept cold to comply with government regulations. Both the trailer's refrigerated cargo area and the refrigerated loading bay may be controlled to approximately the same temperature, but the outside environment may be significantly warmer.
In another example, the loading bay may be part of a building situated in a cold climate. The loading bay may be heated to a comfortable temperature for employees, while the outside temperature may be below freezing.
In yet another example, the loading bay may be in a building located in a hot climate. The loading bay may be air-conditioned to a comfortable temperature for employees, while the outside temperature may be hot and humid.
In each of the above examples, if the cargo area of the truck is not properly sealed against the loading dock door, interface gaps will permit interchange of the warm and cold air. Lack of proper sealing could be caused by an inadequate sealing structure, for example, or by misalignment of the cargo trailer relative to the loading dock.
An inadequate sealing structure includes the failure to properly seal the hinge gap. A hinge gap arises from the pair of swinging panel doors that provide access to the vehicle's rear cargo area. A series of hinges on the vehicle's two rear vertical edges attach the door panels to the vehicle's side wall panels. To access the vehicle cargo area, the two door panels are swung outward away from the rear of the vehicle and stored against the exterior surface of vehicle's side body panels. This can leave a significant hinge gap between the rear of the vehicle and the face of the building.
The interface gaps, including the hinge gap, could in one example allow warm, outside air to flow into a refrigerated vehicle cargo area or loading dock, causing premature food spoilage or noncompliance with governmental temperature regulations. In another example, the interface gaps could cause cold, outside air to flow into the heated space of the building interior, placing extra demands on the heating system and/or resulting in an uncomfortably cold working condition.
Some loading docks have been adapted with devices to provide sealing around the perimeter of the loading dock door frame. One such device comprises foam blocks positioned around the perimeter of the loading bay door. Although the foam provides superior thermal insulation, one noted problem with the foam is that, due to its inherent resiliency, it does not deform very much under load. Therefore, when a trailer backs toward the dock, the trailer must exert a great deal of force to sufficiently compress the foam to effect a good seal. Further, if the trailer bumps into the foam, the foam does not absorb the shock load well. In both circumstances, the trailer loads are transferred directly to the building wall, which, over time, can cause structural damage.
Another sealing device comprised an inflatable bag fitted around the perimeter of the loading dock door frame. Although the inflatable bag solved the problem associated with shock loads, and provided good thermal insulation, the bag often deformed into the passageway of the loading area (e.g., along the sides or top) and created an obstruction hazard for personnel or fork trucks. The exposed air bag material could be a tripping hazard for people loading and unloading the truck. Or, if hit by a fork truck, the bag material could rupture and have to be replaced. The inflatable bags were also prone to puncturing and had to be replaced.